Demands for an optical sensor and a solid-state image pickup device are drastically increasing along with development of science and technology and diffusion of the internet society. At the same time, the market has a high demand for, as an indispensable item to create a new market, an optical sensor and a solid-state image pickup device capable of picking up a still image and a moving image, which have a high sensitivity, a high speed capability, a broad dynamic range, and a broad light wavelength band. In particular, an optical sensor and solid-state image pickup device having a broader dynamic range are demanded in, for example, medical, pharmaceutical, health, and nursing markets, a life science market, and a disaster prevention and crime prevention market indispensable for establishing a safe and secure society.
Examples of the optical sensor and solid-state image pickup device having a broad dynamic range are described in, for example, Patent Document 1.
However, although the optical sensor and solid-state image pickup device described in Patent Document 1 definitely have a broader dynamic range than those of related-art devices, the broadened region of the dynamic range only relates to high illuminance, and the region of the dynamic range remains to be the same as those of the related-art devices for low illuminance. As a result, the optical sensor and solid-state image pickup device described in Patent Document 1 do not satisfy the demand of a market that sometimes requires a broader dynamic range also in a low-light amount region. Thus, satisfaction of such a demand is still a critical problem for the international society to further develop the industry and realize a safer and securer society.
The inventors of this invention have already presented an optical sensor and solid-state image pickup device for solving this problem (Patent Document 2).